The present invention relates to improvements in and relating to methods and apparatus for the sensing of moisture using microwave technologies.
More particularly but not exclusively the present invention relates to the sensing of moisture in timber. However as will be appreciated by those skilled in the engineering and electrical arts the present invention could find application wherever moisture of a non-metallic and particularly an organic material was required. It is envisioned for example that the present invention could find application in the moisture sensing of organic material such as wool or other fibrous materials.
For simplicity, the present invention will be described in respect to its use in the moisture sensing for timber.
Timber in New Zealand and many other countries is dried artificially in kilns. It is important that the dryness of the timber be monitored in situ so that the drying can be terminated at the appropriate level. Current techniques based solely on time typically result in timber being overdried necessitating its subsequent reconditioning. This of course means that time and money is wasted in excessive drying and in the reconditioning.
To alleviate these problems various types of in situ sensors have been proposed. As they are required to be installed within a kiln operating at possibly 180xc2x0 C.-200xc2x0 C. such sensors need to be robust and readily calibrated. Some previous probes have relied on the measurements of capacitance or resistance as an indicator of moisture level. Such probes have been found to be fragile, inaccurate and/or difficult to calibrate.
It is an object of the present invention to provide methods and/or apparatuses for the sensing of moisture level in a material using microwave technologies and to overcome or at least obviate the disadvantage of prior art apparatuses/methods.
Further objects of the present invention may become apparent from the following description.
According to one aspect of the present invention there is provided an apparatus for sensing the moisture content of a material, the apparatus including a wave guide having a linear array of slots in its broadwall, a generator to generate microwave signals over a predetermined frequency range for transmission along the waveguide, a detector suitable for detecting the energy of reflected microwave signals from the waveguide with the material positioned over the slots, a processor to compute a value indicative of the power spectral density of the reflected microwave signals over the predetermined frequency range, wherein the moisture content of the material is determined according to a predetermined relationship between the computed value indicative of the power spectral density and moisture content of the material.
According to another aspect of the present invention, there is provided a method of sensing the moisture of a material, the method including the steps of:
(a) positioning the material over a linear array of slots located in the broadwall of a wave guide;
(b) transmitting one or more microwave signals covering a predetermined frequency range along the waveguide;
(d) detecting the energy reflected from the waveguide of each microwave signal;
(e) computing a value indicative of the spectral density of the reflected microwave signals over the predetermined frequency range; and
(f) determining the moisture content of the material by matching the computed value with a predetermined value of moisture content.
According to a further aspect of the present invention there is provided a moisture sensing arrangement and/or a method of moisture sensing substantially as herein described and/or with reference to the accompanying drawings.
Further aspects of this invention which should be considered in all its novel aspects may become apparent from the following description.